Regulators petition for grid quality

02 October 2012

A larger proportion of intermittent renewable generation will require European grid operators to allow more variation in frequency, but moves to codify this are being resisted by nuclear safety regulators.

A new code for grid operators in the European Union is being developed by the European Network of Transmission System Operators for Electricity (Entsoe). It is intended to resolve "cross-border network issues and market integration issues" one of which requires "facilitating the targets for penetration of renewable generation."

The European Commission has set the target of 20% of electricity to come from renewables, with much of this likely to come from wind. But as well as supplying clean energy, wind power has other effects on the grid system, including that rapid, unpredictable changes in production cause grid transmission voltages and frequencies to vary.

Power generators are currently required to supply at an average of 50 Hz, obliging them to balance out variations of up to 1 Hz that occur for technical reasons from time to time - and take their power plant offline if they can't operate in that range. This is too stringent for large scale renewable generation and so the draft code being developed would allow frequencies to drop as low as 47.5 Hz.

In a letter to the Agency for the Cooperation of Energy Regulators yesterday the Western European Nuclear Regulators Association (WENRA) said this has "the potential to negatively affect nuclear safety" because "the definition for the range of frequency and voltage is too large." Under nuclear safety legislation the lowest frequency allowed for safety-related equipment is 48 Hz and a frequency below that means, for example, that a coolant pump might operate too slowly.

Entsoe has said that nuclear power is expected to make up a significant portion of future European energy mix, with the newest plants predicted online until 2080. However, new nuclear power plants must be able to fit in with other elements of the mix, which is sure to include a lot of intermittent and variable wind and solar power in line with "European political goals."

Entsoe said that it had engaged extensively with nuclear technology firms and "recent feedback from manufacturers confirmed that the requirements of the network code are in general technically feasible." It concluded that a general exemption from the code for nuclear power plants is "not justified."

WENRA's letter petitioned for the code to be amended with a line saying, "For nuclear power plants, nuclear safety considerations are prioritized in the case of a conflict between nuclear safety considerations and the network code."